As a method for producing a magnetic disk substrate for hard disk devices (HDD), a method for producing a magnetic disk substrate, which includes performing a plating pretreatment prior to applying electroless nickel plating to an aluminum substrate, and applying electroless nickel plating to the aluminum substrate that has been subjected to the plating pretreatment, is typically known.
In the plating pretreatment, a cleaning treatment, an etching treatment, a desmutting treatment, and a zincate treatment are performed. As the zincate treatment, a double zincate treatment is known that includes performing a de-zincate treatment following a first zincate treatment, and then performing a second zincate treatment.
When the surface of an electroless nickel plating film has a large number of waviness, protrusion defects called nodules, or recess defects called pits, there is a possibility that such defects may not be able to be completely removed in a polishing step, and thus may remain as defects. Thus, it is necessary to develop an electroless plating method that can obtain a smoother surface of a plating film.
For example, Patent Literature 1 describes a method of smoothing the surface of a plating film by including metal ions of Group IV of the periodic table in a nitric acid bath used in a desmutting treatment in order to obtain a surface of a plating film without protrusion defects.